The present invention relates to a materials-handling plant which can be alternately converted and operated to produce asphalt and remediate contaminated soil. Particularly, the present invention relates to a materials-handling plant which, in the production of asphalt, can be converted between a batch plant and a high-capacity drum mix plant and, when operating as a soil remediation plant, can treat and remediate contaminated soils, particularly those containing hydrocarbon products and hydrocarbon chemicals such as PCBs, in a thermally efficient, environmentally compatible and safe manner.
In the production of asphalt, a single production plant will typically consist of either a batch plant or a high-capacity drum mix plant. In a batch plant, aggregate is disposed in a rotatable drum and a burner supplies hot gases of combustion within the drum, typically in counterflow relation to the direction of flow of the aggregate, to dry the aggregate. The dried aggregate is then discharged from the drum into a batch tower. In the batch tower, the aggregate is sized and then combined with hot asphalt in a mixing section for delivery to a truck for transportation to the job site.
In a typical drum mix plant, the dried aggregate is emptied from the drying section of the drum into a contiguous drum mixing section. In the mixing section, dried aggregate, asphalt, recycled asphalt material, if added, and mineral filler are mixed to form the hot mix asphalt product. The hot mix section of the drum is closed and vapors, including any blue smoke and odors, are recycled into the burner, where they are incinerated and converted into fuel. The hot mix is then discharged from the drum for delivery to a truck or to a storage silo for later delivery to the job site.
In both cases, exhaust gases from the drum are passed through a primary collector for separating the large particles from the exhaust gas stream, the latter then passing into a baghouse for further separation of the finer particles from the exhaust gas stream. The particles collected from the primary separator and the baghouse are returned to the mixing section of the drum mixer or to the hot aggregate elevator tower in the batch plant.
The advantages of both continuous drum mix and batch plant operations have been recognized and combined in a single plant. Thus, for the plant to operate in a batch mode, the aggregate is dried in the drum and removed to the batch tower, where it is mixed with the asphalt. The particulate material separated out by the primary collector and baghouse may be added to the drum mixer. When it is desired to operate the plant in a drum mix mode, the aggregate is dried as usual and then discharged into the contiguous mixer section of the drum for mixing with asphalt. The hot asphalt mix is then discharged from the drum mixer and conveyed along a conveyor into a hot mix storage silo. Thus, by providing a drum having both batch and drum mixing capability, as well as equipment for batch operations, i.e., the hot elevator tower and batch tower, and for drum mixing operation, i.e., a slat conveyor and storage silo, the advantages of both batch and drum mixing operations have been achieved in a single asphalt plant.
It has now been recognized according to the present invention that processes and equipment for the treatment of contaminated soils, for example, those soils containing hydrocarbon products and hydrocarbon chemicals such as PCBs, have certain similarities with the foregoing described processes and equipment for the production of asphalt. Such equipment and processes are described, for example, in co-pending patent application Ser. No. 07/627,243 in which there is disclosed apparatus and methods for remediating contaminated soils, including a rotating drum for receiving the hydrocarbon-contaminated soil. By operating the drum within certain temperature limitations, the hydrocarbons within the soils can be oxidized within the drum. Thus, as set forth in the above-mentioned U.S. patent application, contaminated soil is supplied the upper end of an inclined rotating drum and hot gases of combustion are supplied the opposite end, whereby the contaminated soil is remediated by volatilization of the contaminants. The clean soil is discharged from the drum for disposition into a mixer cooler, where the remediated soil is mixed with water and other particulate material recombined with the soil, as described below. The exhaust gases from the drum are passed through a primary collector and then through a baghouse for separation of the particulate matter from the gases. The separated particulate matter is separately remediated in the baghouse, for example, by the system described and illustrated in co-pending application Ser. No. 07/627,243, filed Dec. 14, 1990, the subject matter of which is incorporated herein by reference. That remediated particulate matter may be conveyed to the mixer cooler for combination with the remediated soil from the drum. The gases from the baghouse are then passed through a thermal oxidizer where any residual contaminants are oxidized. The gases from the baghouse are, however, first placed in heat exchange relation with the exhaust gases from the thermal oxidizer for thermal efficiency purposes.
It has been discovered according to the present invention that a single materials-handling plant can be provided which can be converted for either of the aforedescribed two different types of asphalt production operations as well as a plant for soil remediation. That is to say, using equipment common to each of the three processes and additional equipment as necessary to each of the processes, the single plant may be converted for soil remediation or asphalt production either by continuous drum mix or batch processes. To achieve the foregoing, the major elements of the single plant hereof for use in soil remediation and the production of asphalt as described are the following: (a) a drum/mixer; (b) a hot aggregate elevator and batch tower; (c) a hot mix storage silo and associated conveyor; (d) a primary separator and a baghouse, collectively sometimes called a separator; (e) a mixer cooler; and (f) a thermal oxidizer, together, of course, with associated conveyors, controls, ducting and the like.
To operate this system in a batch mode for the production of asphalt, aggregate is introduced into the drum and dried by contact with the hot gases of combustion from the drum burner. The aggregate is discharged from the drum and conveyed by the elevator into the batch tower for sizing and mixing with hot asphalt. For operation as a drum mixer plant, the aggregate is introduced into the drum, dried, and is then discharged into the drum mixing section, where the dried aggregate is combined with asphalt, recycle asphalt and other material. The hot mixed asphalt is then conveyed to the storage silo for subsequent use. In both cases, the primary collector and baghouse are used to separate particulate matter from the exhaust gases of the drum and convey the particulate matter to the batch tower or into the hot mixing zone of the drum when in the drum mixing mode. To employ this system as a soil remediation plant, the contaminated soil is introduced into the drum and the hot gases of combustion volatilize the contaminants. The remediated soil is discharged from the drum into the mixer cooler where water is applied to the remediated soil. The exhaust gases from the drum flow through the primary collector and the baghouse similarly as in asphalt production. The particulate material separated out in the primary collector and the baghouse is treated at high temperature to volatilize remaining contaminants by mixing with the remediated soil and in the mixer cooler being blended with the remediated soil. The hot gases leaving the baghouse, however, are passed through a thermal oxidizer to oxidize the contaminants in the gases. Before exhausting the gases exiting the thermal oxidizer, they are placed in heat exchange relation with the incoming gases from the baghouse to afford thermal efficiency to the process.
In a preferred embodiment according to the present invention, there is provided a materials handling plant having a rotatable drum, a burner for flowing hot gases of combustion through the drum for drying material in the drum, a separator for separating out particulate material in gases exhausted from the drum, a thermal oxidizer for oxidizing residual contaminants in the gases exhausted from the separator, means for mixing material dried in the drum with asphalt to form an asphalt mix and a means for combining particles separated from the exhaust gases and material from the drum, a method of operating the plant for alternately producing an asphalt mix and remediating contaminated soil, comprising the steps of (a) when the plant is operated to produce an asphalt mix, (i) supplying material in the form of aggregate to the drum, (ii) drying the aggregate within the drum, (iii) flowing particulate-laden gases from the drum through the separator for separation into an exhaust gas stream and a particle stream; (iv) returning the particles of the particle stream to the aggregate, and (v) combining the aggregate with asphalt to produce an asphalt mix and (b) when the plant is operated to remediate contaminated soil, (i) supplying material in the form of contaminated soil to the drum, (ii) heating the soil in the drum to volatilize the contaminants, (iii) flowing particulate-laden gases from the drum through the particle separator for separation into a first exhaust gas stream and a first particle stream, (iv) subjecting the particles of the first particle stream to an elevated temperature sufficient to volatilize residual contaminants and provide contaminant-free particles, (v) combining the heated soil and contaminant-free particles and (vi) passing the first exhaust gas stream through a thermal oxidizer to destroy residual contaminants, leaving a substantially clean exhaust gas stream.
In a further preferred embodiment according to the present invention, there is provided a materials-handling plant comprising a rotatable drum and a burner for flowing hot gases of combustion through the drum, the rotatable drum having a drying section and a mixing section downstream from the drying section in the direction of material flow, a primary separator for separating out particulate material in gases exhausted from the drum, a baghouse for separating fine particulate material in gases exhausted from the primary separator and a thermal oxidizer for oxidizing contaminants in gases exhausting from the baghouse. Means are provided for mixing aggregate material and asphalt to form an asphalt mix and a mixer/cooler for receiving soil discharged from the drying section of the drum and mixing the discharged soil with water.
Accordingly, it is a primary object of the present invention to provide apparatus and methods in a single plant for alternately remediating contaminated soil and producing asphalt either by continuous drum mix or batch processes.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.